The present invention relates to network systems using the Internet Protocol (IP) and equipped with a plurality of routers for receiving packets from a plurality of hosts on a Local Area Network (LAN). More specifically, the invention provides for a dynamic assignment of the routers to hosts and authorizes load balancing over the hosts, the routers being seen by the hosts as a single default router.
Local area networks (LANs) are usually connected with each other through one or more routers so that a host i.e., a Personal Computer, a Work Station, a Server or any equivalent device on a given LAN can communicate with other hosts on different LANs using the Internet Protocol (IP). Typically, the host is able to recognize only the devices on its LAN. When it receives a request to send a data packet to an address that it does not recognize, it must go to a router which determines how to direct the packet from the host towards the IP destination address. However, a router may, for a variety of reasons, become inoperative (e.g., a power failure, rebooting, scheduled maintenance, etc.). When this happens, the host that used to communicate through the inoperative router may still reach other LANs if it can forward packets to a different router, still active, connected to its LAN.
There are a number of methods that an end-host can use to determine its first hop router towards a particular IP destination. They include running a dynamic routing protocol such as Routing Information Protocol (RIP) or the Router Discovery of the Internet Control Message Protocol (ICMP). These are examples of protocols that involve dynamic participation by the host. The host in a RIP system receives the periodic routing protocol packets broadcast by the various routers. If a router stops sending protocol packets, the host assumes that the router is no longer operative and stops sending data through that router. Unfortunately, routing protocol packets contain relatively large amounts of data including all the specific routes known by the routers. Because the host periodically receives these rather large packets, the system bandwidth is reduced.
In ICMP Router Discovery, the host keeps track of operative routers by listening for router reach ability messages. These messages contain a list of IP addresses of usable routers together with preference values for those routers. Because these messages are relatively small (in comparison to routing protocol packets received by the host in RIP) and are not coupled time-wise with any routing protocol, the bandwidth utilization is improved in comparison with RIP.
However, running a dynamic routing protocol on every end-host may be unfeasible for a number of reasons, including administrative overhead, processing overhead, security issues, or lack of a protocol implementation for some platforms. Thus, a widely used and simpler approach is to have the host recognizing only a single xe2x80x9cdefaultxe2x80x9d router. In this approach, the host is configured to send data packets to the default router when it needs to send packets to addresses outside its own LAN. It does not keep track of available routers or make decisions to switch to different routers. This requires very little resources on the host side, but the obvious consequence is, if the default router fails, that the host can no longer forward packets outside of its own LAN.
Therefore, to overcome this serious drawback of the default router approach which creates a single point of failure, a method known as the Hot Standby Router Protocol (HSRP), subject of the request for comments #2281 (rfc2281) of the Internet Engineering Task Force (IETF) and object of the U.S. Pat. No. 5,473,599 under the title xe2x80x98Standby Router Protocolxe2x80x99 has been devised. The goal of the protocol is to allow hosts to appear to use a single router and to maintain connectivity even if the actual first hop router they are using fails. Multiple routers, most often two, participate in this protocol and together create the illusion of a single virtual router. The protocol insures that one and only one of the routers is forwarding packets on behalf of the virtual router. The router forwarding packets is known as the active router. A standby router is selected to replace the active router should it fail. The protocol provides a mechanism for determining active and standby routers, using the IP addresses on the participating routers. Although HSRP does well what it has been designed for, i.e., provides a mechanism to support non-disruptive fail over of IP traffic in certain circumstances, in particular, to protect against the failure of the first hop router when the source host cannot learn the IP address of the first hop router dynamically, it presents the specific drawback of requiring two routers one being always in standby, waiting for the other one to die, while it could have actively participated to the forwarding of the traffic.
An alternate approach, also aimed at avoiding the single point of failure of the default router is known under the name of Virtual Router Protocol (VRRP) subject of IETF rfc2338. VRRP specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The VRRP router controlling the IP address(es) associated with a virtual router is called the Master, and forwards packets sent to these IP addresses. The election process provides dynamic fail-over in the forwarding responsibility should the Master become unavailable. Any of the virtual router""s IP addresses on a LAN can then be used as the default first hop router by end-hosts. The advantage gained from using VRRP is a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host. VRRP provides a function similar to the previously described HSRP protocol.
Besides the availability issue here above discussed, another important issue on a LAN comprising a plurality of routers and hosts is the ability to perform an outbound load balancing, i.e., to effectively balance the hosts related traffic over the multiple routers so as each of them is always processing a fair share of the outbound global traffic. Ideally, this should stay true even though hosts related traffic may drastically change over time. To cope with this requirement a static reconfiguration would be necessary with the solutions here above described. This may become unfeasible if adjustments need to be performed frequently say, on a daily basis just because peaks of traffic are regularly observed on some of the hosts while others are quiet.
As a consequence of the above, it would be desirable to have a network system in which the hosts are, for the sake of simplicity, not dynamically involved in router selection, while being able to dynamically reconfigure the network so as, firstly, to dynamically cope with the fluctuations of the traffic over time and, secondly, to handle router failures thus offering a non disruptive service while traffic remains well balanced over the routers in all circumstances.
Thus, it is a broad purpose of the invention to allow, on a LAN, a non disruptive fail over of the outside IP traffic.
It is a further purpose of the invention to allow that hosts traffic be always spread on all available routers.
It is another purpose of the invention to permit a dynamic reconfiguration of the network if a router fails or is added, or must be changed or if hosts traffic changes significantly.
It is yet another purpose of the invention to allow that the hosts be not involved in the router selection.
Further advantages of the present invention will become apparent to the ones skilled in the art upon examination of the drawings and detailed description. It is intended that any additional advantages be incorporated herein.
A method and system are here disclosed for dynamically assigning, on a Local Area Network, through a mediator, a plurality of active routers to a plurality of hosts. The mediator, the hosts and the routers have each a unique address on the LAN for handling through the routers, data packets from the hosts destined to remote users not connected on the LAN. The method proceeds by steps of storing initially in the hosts, as default address, the address of the mediator. Then, upon sending from a particular host a first data packet towards one of the remote users not connected on the LAN, a request is first issued from that particular host, using the address of the mediator, for the purpose of being assigned a particular router. In response to the request, mediator selects one among those of the routers that are active and informs the host which may then forward the first data packet to the selected router. After which all subsequent data packets from that host are sent directly to the selected router. The same is done for each host connected on the LAN.
The mediator may decide to reassess the router to host assignment any time if significant changes are observed such as the failure of a router, the removal or the addition of a router to the pool of routers or a drastic modification of the host generated traffic.
Thus, the method and system of the invention allow to insure that IP traffic generated from the hosts for users not connected on the LAN is never interrupted and always well spread over the active routers in all circumstances without having to reconfigure the hosts.